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On her daily commute to the scientific station, scientist the researcher crouches near a small water body covered by thick plants and collects a small plastic sound recorder.

The device was left there overnight to record the distinctive croaks of the Fowler's snouted treefrog, known by local scientists as an invasive species with consequences that scientists are starting to comprehend.

Although abounding with unique wildlife – including ancient giant tortoises, swimming lizards, and the well-known birds that inspired Darwin's theory of evolution – the island chain off the coast of Ecuador had long remained free of amphibians.

During the 1990s, this changed. Several small tree frogs made their way from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic research suggest that, over the years, there have been multiple accidental arrivals to the islands, and the frogs now have a strong presence on two islands: multiple locations.

The population is expanding so quickly that scientists have been struggling to monitor, calculating numbers in the millions on every island, across developed and farming areas, but also in the protected natural reserve.

When the biologist tagged amphibians and attempted to recapture them in the following week and a half, she could find only a single marked frog from time to time, suggesting their populations were enormous.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," says San José. "I am quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The amphibians' abundance is clear from the sound disruption they cause. "The number of frogs and the sound – it's truly incredible," comments San José.

For the scientists, their nocturnal mating calls are helpful in estimating their existence in remote areas, using audio devices like the one near the workplace.

But local farmers say the sounds are so loud they keep them up at night.

"In the wet season, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, observing the first frogs in the region," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unclear

The sound isn't the primary problem, however. While the amphibians has been in the islands for nearly 30 years, experts still know very little about its impact on the archipelago's precariously balanced land and water environments.

On islands, it is very typical for invasive species to thrive, as they have few of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are significantly affecting the safety of its endemic ones.

A 2020 study suggests the invasive frogs are voracious bug consumers, and might be disproportionately eating rare bugs found only on the islands, or reducing the food sources of the islands' rare birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The island frogs have exhibited some atypical traits, including living in brackish water, which is rare for amphibians.

Their development process is also extremely variable, with some larvae turning into frogs very rapidly and others taking a extended period: San José observed one which remained as a tadpole in her lab for half a year.

"We truly don't know this part," she says, concerned the tadpoles could be impacting the region's freshwater, a very limited commodity in Galápagos.

Techniques to control the frogs in the early 2000s were largely ineffective. Conservation officers tried capturing significant quantities by hand and gradually increasing the salt content of ponds in vain.

Studies indicates spraying caffeine – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't necessarily safe for other uncommon Galápagos organisms.

Lacking solutions to more of the basic issues about their lifestyle and impact, removing the amphibians might not even be the right way to proceed, says San José.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and DNA examination will help her group make sense of the invader, financial support for the research has been hard to come by.

"Everyone wants to give funding for protecting frogs," says San José. "But it's harder to find funding for an introduced frog that you might want to control."